The extension aims to be as theme-friendly as possible. The dock appearence is inherited from the default dash so basic theme support is always granted. However, some features has to be direclty supported by the theme. There are some themes supporting the extension.
Adding support to a theme for the Dash to Dock extension is easy: the dash is put inside a container actor named #dashtodockContainer so the extended dash can be targeted without conflicting with the default dash. There are some additional css classes that theme writers can exploit in order to support the extension better:
.running1, .running2, .running3, .running4: like the default .running style but based on the number of windows of the application. The .running4 class targets 4 and more windows. All classes are applied to the app-well-app actors.
.focused: applied to the .app-well-app actor of the currently focused application.
.extended: applied to the #dashtodockContainer actor when the dock height is extended to the whole vertical space.
Since version 29, a custom theme previously released as a separate theme is built in the extension and optionally applied through the .dashtodock class of the #dashtodockContainer.
Below is a css code snippet showing how the dock can be customized